It has long been the practice in motor vehicles, such as automobiles and trucks, to suspend engines and other heavy components that generate vibrations when operating on resilient mounts that isolate and damp the vibration from reaching the passenger compartment of the vehicle. It is desirable in such circumstances to provide a mount that is relatively soft for low amplitude higher frequency vibrations, such as those produced while an engine is operating at idle speed. Making the mount too soft, however, results in a structure that may not be capable of damping the motion of a heavy mass, such as the engine, when the vehicle is traveling over a bumpy road.
The competing requirements for a mount that is soft enough to isolate low amplitude vibrations generated by an engine at idle, and yet is robust enough to damp and limit the movement of an engine relative to the vehicle chassis when the vehicle is encountering a bumpy road surface, have caused the designers of resilient mounts to employ hydraulic fluid flowing between multiple chambers within the mount, together with judiciously sized orifice tracks and fluid valve arrangements providing fluid communication between the chambers, to provide mounts that exhibit different dynamic stiffness characteristics dependent upon the magnitude and frequency of the vibratory input to the mount. Such mounts are known as controlled rate dip mounts.
The construction of prior resilient controlled rate dip mounts, has required relatively complicated internal chambering, track configurations, and valve arrangements that result in considerable and undesirable complexity and cost to achieve acceptable rate dip performance of the mount. In addition, physical constraints imposed by prior mount constructions require that compromises be made that result in less than ideal performance of the mount at one or more of the operating conditions.
What is needed, therefore, is an improved resilient mount, offering a more straight-forward construction and improved passive dip rate performance, in comparison to prior hydraulic mounts.